Oral delivery of medicaments to treat disorders such as asthma, emphysema and chronic bronchitis has been, for many years, reliably and effectively accomplished through the use of pressurized metered dose inhalers (PMDIs). Such inhalers provide a stream of atomized medicament inhaled directly into the affected air passageways and lungs to afford rapid relief from the symptoms of such disorders.
As an alternative to PMDIs, dry powder inhalers (DPIs) have received considerable attention because of their propellant-free composition and their relative ease of operation compared to PMDIs. DPIs can be used for oral and nasal administration and may be presented with the drug formulation pre-metered as capsules (unit-dose inhaler), blisters and cartridges (multi-unit dose inhaler) or as bulk material in a reservoir (multi-dose inhalers).
A necessary design feature of PMDIs and multi-dose DPIs is that they contain more formulation than strictly required to expel the labeled number of actuations/doses. A potential problem which may be particularly acute for PMDIs is dose inconsistency beyond labeled number of actuations/doses. A patient unknowingly using a PMDI or multi-dose DPI beyond the recommended number of doses may risk not receiving the correct drug dose with possibly dangerous consequences.
To avoid this problem, it is desirable to include a counter or indicator integrally with the inhaler to count and display to the user the number of doses remaining within the inhaler. This will allow the user sufficient warning as to when the inhaler is running low and should, therefore, be replaced so as to avoid the potential for sub-therapeutic dose administration. The counter or indicator should be simple in design, reliable in operation and easy to read and interpret.